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onsemi UC3842BD
- Part No.:
- UC3842BD
- Manufacturer:
- onsemi
- Category:
- DC DC Switching Controllers
- Package:
- 14-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
UC3842BD.pdf
- Description:
- IC REG CTRLR PWM CM 14-SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,433
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Product details
Overview
UC3842BD from onsemi is a high-performance current-mode PWM controller IC designed for off-line and DC-DC power converters. It features a trimmed 250 kHz oscillator, 5.0 V ±1% reference, undervoltage lockout (16 V ON / 10 V OFF), and a 1.0 A totem-pole output stage optimized for driving power MOSFETs in flyback and forward topologies.
For engineers reviewing the UC3842BD datasheet, pinout, applications, or equivalent options, this device is selected for cost-sensitive, fixed-frequency AC-DC adapters, industrial SMPS, and isolated DC-DC modules requiring precise peak-current control, cycle-by-cycle limiting, and stable startup under wide input voltage ranges.
Technical Context
The UC3842BD implements fixed-frequency current-mode control using an internal oscillator programmed via RT/CT, a high-gain error amplifier with 90 dB open-loop gain and 1.0 MHz unity-gain bandwidth, and a latching PWM comparator that terminates switch conduction when sensed current exceeds the error-amplifier-derived threshold. Its architecture supports automatic feed-forward compensation and subharmonic oscillation mitigation via external ramp injection.
It integrates dual undervoltage lockouts - one on VCC (16 V/10 V hysteresis) and one on Vref (3.6 V/3.4 V) - ensuring robust start-up in offline applications. The SOIC-8 package (D suffix) uses shared ground for control and power circuits, while the SOIC-14 variant separates VC and power ground to reduce noise coupling into the control loop.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | Guaranteed 250 kHz at 25°C; programmable up to 500 kHz via RT/CT; enables stable timing in compact, high-efficiency converters. |
| Reference Voltage | 5.0 V ±1% at TJ = 25°C; supplies precise bias for RT/CT charging and external circuitry; supports accurate duty-cycle regulation. |
| UVLO Thresholds | 16 V turn-on / 10 V turn-off; ensures reliable bootstrap startup in 85–265 VAC offline designs without external supervision. |
| Output Drive | ±1.0 A peak sink/source capability; directly drives gate capacitance of medium-power MOSFETs without buffer stages. |
| Current Sense Threshold | 1.0 V max clamp level; sets absolute peak switch current limit independent of error amplifier output during overload. |
| Error Amplifier Gain | 90 dB typical open-loop DC gain; provides high loop gain for tight output voltage regulation across line/load variations. |
| Max Operating Temp | +70°C ambient; suitable for commercial-grade power supplies where thermal derating is managed via PCB layout and heatsinking. |
Pinout & Package
UC3842BD is supplied in an 8-pin SOIC surface-mount package (Case 751, D suffix). Pin functions are validated per onsemi datasheet Rev. 12 (2008).
| Pin | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Compensation | Error amplifier output; connects to RC network for loop stability tuning and phase margin control. |
| 2 | Voltage Feedback | Inverting input of error amplifier; monitors regulated output via resistor divider to maintain setpoint accuracy. |
| 3 | Current Sense | Input to PWM latch comparator; senses MOSFET source current via shunt resistor for cycle-by-cycle current limiting. |
| 4 | RT/CT | Oscillator timing node; RT sets charging current, CT sets frequency and deadtime; defines switching frequency and max duty cycle. |
| 5 | GND | Common ground for control circuitry and power stage return; critical for noise immunity in current-sense path. |
| 6 | Output | Totem-pole gate driver output; delivers ±1.0 A to charge/discharge MOSFET gate; requires low-inductance layout. |
| 7 | VCC | Positive supply input; powers internal bias, reference, and logic; must exceed 16 V to exit UVLO and sustain operation. |
| 8 | Vref | 5.0 V reference output; sources current to RT/CT network and may power auxiliary circuitry; short-circuit protected. |
Key Features
| Feature | Design Value |
|---|---|
| Trimmed oscillator | 250 kHz frequency guaranteed at 25°C; ±10% tolerance up to 250 kHz eliminates need for post-manufacture trimming. |
| Latching PWM | Single-pulse-per-cycle operation prevents multiple switching events; ensures predictable current limiting during fault conditions. |
| High-current totem pole | 1.0 A peak drive capability reduces external gate driver requirements; supports fast MOSFET switching with <150 ns rise/fall times. |
| Undervoltage lockout with hysteresis | 16 V/10 V thresholds prevent erratic startup in brownout conditions; eliminates need for external supervisor IC. |
| Internally trimmed 5.0 V reference | ±1% initial accuracy at 25°C; enables precise RT/CT timing and stable feedback loop operation without external references. |
Applications
| AC-DC Adapter | Flyback SMPS |
|---|---|
|
Use Scenario: 12 V/2 A universal-input (85–265 VAC) wall adapter for consumer electronics. IC Role / Device Role / Timing Role: Primary-side PWM controller regulating output via optocoupler feedback; sets 65–100 kHz switching frequency. Use Value: Enables compact design with minimal external components; UVLO ensures reliable startup from low-line conditions. |
Use Scenario: Isolated 5 V/5 A industrial power supply with overcurrent protection. IC Role / Device Role / Timing Role: Current-mode controller implementing primary-side sensing and cycle-by-cycle current limiting. Use Value: Provides inherent slope compensation readiness and stable regulation under variable load and input voltage. |
| Offline Battery Charger | DC-DC Forward Converter |
|
Use Scenario: 24 V lead-acid battery charger powered from 120 VAC mains. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller managing bulk charging stage with constant-current regulation. Use Value: Latching PWM and 1.0 V current sense clamp deliver repeatable overcurrent shutdown without secondary sensing. |
Use Scenario: 48 V to 12 V telecom DC-DC converter with tight output tolerance. IC Role / Device Role / Timing Role: Primary-side controller synchronizing MOSFET gate drive with transformer reset timing. Use Value: High-gain error amplifier (90 dB) and low-noise reference support ±1% output regulation across temperature. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar current-mode PWM controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC3842N | PDIP-8 package; higher thermal resistance (100°C/W vs. 178°C/W for SOIC-8); same electrical specs and pinout. | Suitable for prototyping or through-hole assembly; less suited for high-density SMT production or thermally constrained layouts. | Select UC3842N only when manual soldering or breadboarding is required; UC3842BD preferred for volume SMT manufacturing. |
| TL494CN | Fixed-frequency voltage-mode controller; dual-output, adjustable deadtime, no integrated reference; requires external 5 V supply. | Better for push-pull or half-bridge topologies; lacks built-in current sensing and UVLO hysteresis of UC3842BD. | Choose TL494CN when dual complementary outputs or flexible deadtime control are needed; not drop-in for UC3842BD flyback designs. |
Compared with UC3842N and TL494CN, the UC3842BD offers superior integration for single-switch current-mode converters - combining reference, UVLO, oscillator, and 1 A gate drive in an SOIC-8 footprint - reducing BOM count and layout complexity in cost-sensitive AC-DC applications.
Availability
UC3842BD is available at Aetrix Electronics and suitable for AC-DC adapters, industrial SMPS, and offline battery chargers requiring stable component supply, long-lifecycle support, and consistent parametric performance across production batches.
Supply support for UC3842BD includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
onsemi (formerly ON Semiconductor) is a global semiconductor manufacturer specializing in energy-efficient power management, analog, and sensor solutions for automotive, industrial, and cloud infrastructure markets.
The UC384xB series was developed to deliver high-performance, low-cost current-mode PWM control for mainstream offline and DC-DC power conversion, emphasizing ease of use, minimal external components, and robust operation across commercial temperature ranges.
FAQ
What is the maximum operating frequency of the UC3842BD?
The UC3842BD oscillator is guaranteed to operate at 250 kHz at 25°C and supports current-mode operation up to 500 kHz via external RT/CT selection. Frequency accuracy degrades with temperature and supply voltage variation; design margins should account for ±10% tolerance at 250 kHz and wider spread at higher frequencies.
Does the UC3842BD require an external current-sense resistor?
Yes, the UC3842BD requires an external current-sense resistor (RS) connected between the MOSFET source and ground. Pin 3 monitors the voltage drop across RS to implement cycle-by-cycle current limiting; typical values range from 0.1 Ω to 1.0 Ω depending on peak current requirements.
Can the UC3842BD be used in a voltage-mode control configuration?
No - the UC3842BD is inherently a current-mode controller. Its PWM latch resets based on sensed inductor current, not error amplifier output alone. Voltage-mode operation would require external circuitry to override the current-sense comparator, compromising safety and violating the intended architecture.
What is the purpose of the Vref pin (Pin 8) on the UC3842BD?
Pin 8 provides a regulated 5.0 V ±1% reference output that supplies charging current to the RT/CT timing network. It can also power auxiliary circuitry (e.g., optocoupler LED, feedback divider bias), but total load must remain within 20 mA to avoid regulation error or thermal stress.
How does the UC3842BD handle overcurrent conditions?
The UC3842BD implements latching cycle-by-cycle current limiting: when the voltage at Pin 3 exceeds 1.0 V, the PWM latch resets and holds the output low until the next oscillator cycle. This provides immediate, repeatable shutdown during overload or short-circuit events without requiring external fault latches.
UC3842BD Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- -
- Package/Case:
- 14-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Output Type:
- Transistor Driver
- Function:
- Step-Up, Step-Up/Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Boost, Flyback
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 10V ~ 30V
- Frequency - Switching:
- Up to 500kHz
- Duty Cycle (Max):
- 96%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-SOIC
UC3842BD FAQ
1.How can I place an order for UC3842BD through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3842BD on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for UC3842BD reliable?
The price and inventory of UC3842BD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3842BD is usually 5 days.
3.What payment methods are accepted for UC3842BD?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3842BD transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3842BD?
UC3842BD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3842BD order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for UC3842BD?
For technical support, including UC3842BD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3842BD requirements.
6.How does Aetrix verify that UC3842BD is sourced from the original manufacturer or authorized distributors?
All UC3842BD products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that UC3842BD meets industry standards.
7.What is the process for return or replacement of UC3842BD?
All UC3842BD units undergo pre-shipment inspection (PSI). If there is an issue with UC3842BD, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The UC3842BD part is unused and in its original packaging.
Return procedure for UC3842BD:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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